Electrodes



J. R. HALL ETAL 3,291,734

ELECTRODES Dec. 13, 1966 Filed Jan. 8, 1962 3 Sheets-Sheet 1 3y MM, ALM/7 f Q01/WM,

Dec. 13, 1966 J. R. HALL ETAL ELECTRODES 5 Sheets-Sheet 25 Filed Jan. 8, 1962 Dec. 13, 1966 J. R, HALL ETAL 3,291,714

ELECTRODES Filed Jan. 8, 1962 I5 Sheets-Sheet I5 ffl/( ,y

By www] QM/yf United States Patent O 3,291,714 ELECTRODES John Robert Hall, Blackburn, Victoria, and Johannes Theodorus Van Gemert, Lalor, Victoria, Australia, assignors to Imperial Chemical Industries of Australia and New Zealand Limited, Melbourne, Australia, a corporation of Australia Filed Jan. 8, 1962, Ser. No. 164,854 Claims priority, application Australia, Jan. 13, 1961, 363/61 25 Claims. (Cl. 2114-256) This invention relates to electrodes for use in electrolytic cells.

In the electrolytic cells for the electrolysis of brine or in direct current generators such as fuel cells, the cathodes most commonly used at present are made from iron or steel. Such electrodes, because of their low corrosion resistance in acidic media, impose limitations on the cell design; thus, c g., they must not come into direct contact with the anolyte because of the rapid attack of halogens on iron in aqueous medium. Consequently, these electrodes are unsuitable for use in bipolar cells.

Furthermore, it is well-known that the voltage drop between the anode and cathode in an electrolytic cell in which gases are generated at the electrodes is made up of a number of components, one of which is the overvoltage for the particular gases and for the particular electrodes concerned.

In industrial applications of electrolytic cells it is Very important from the point of view of operating costs to reduce to a minimum the voltage drop for an electrolytic process and this therefore leads to the use of electrodes having the lowest overvoltage potentials in the system employed. For example, it is customary in alkaline cells involving evolution of hydrogen and oxygen to use a nickel anode and an iron cathode.

In certain cells it is import-ant for reasons other than operating cost to reduce the voltage drop to a minimum. Thus in certain cases the constructional design of the cell may be materially simplied by reducing the voltage drop by even as low as 0.1 volt.

Recently, electrodes have been developed which overcome the corrosion problems associated with steel electrodes and which do not need regular replacement as graphite electrodes do and which are resistant to both anolyte and catholyte, thus permitting the design of bipolar cells assembled into multi-cell units. Such cells are described in Australian Patent No. 230,799. In these multicells a bipolar titanium electrode forms the partition wall separating two adjacent cells, one side of the electrode being the cathode of one cell and the other side of the electrode being the anode of the adjacent cell. As a result these cells are extremely compact, require no costly and energy-wasting electrical connections between anodes and cathodes, have a small electrode gap and consequently a low potential drop through the electrolyte, a small potential drop through the electrode itself and permit high current densities; hence these cells have a low overall operating voltage and high production capacity per unit floor area and capital cost. However, titanium sheet has a relatively high hydrogen overvoltage.

It is also known that nely divided platinum or palladium coatings deposited on the iron support of the electrode overcome 'the disadvantages associated with steel electrodes by reducing the hydrogen overvoltage, but such deposits are very expensive and not always durable enough to be economical.

We have now discovered that certain .alloys can be deposited on metallic, particularly steel, electrodes in general and on titanium core electrodes in particular to ICC form electrodes of considerable durability which have a reduced hydrogen overvoltage when used as cathodes in electrolytes.

Accordingly we provide an electrode comprising ya support formed from a metal suitable for the construction of solid electrodes, at least a portion of the surface of which is conductively covered by a coating of an alloy consistingof a metal selected from the group of molybdenum and tungsten alloyed with iron.

We also provide an electrode comprising a I support formed from Va metal suitable for the construction of solid electrodes, at least a portion of the surface of which is conductively covered by a coating of an alloy consisting of molybdenum alloyed with a secondary metal selected from the group of nickel and cobalt.

A further embodiment of this invention consists in an electrode comprising a support formed from a metal suitable for the construction of solid electrodes, yat least a portion of the surface of which is conductively covered by a coating of a ternary alloy consisting of a primary metal selected from the group of molybdenum and tungsten alloyed with two secondary metals selected from the group of cobalt, nickel and iron.

We furthermore provide an electrolytic cell having a cathode formed from a metal suitable for the construction of solid electrodes, a portion or the whole of the surface of which is conductively covered by either a coating of an alloy consisting of a primary metal selected from the group of molybdenum and tungsten alloyed with iron or, alternatively, covered by a coating of an alloy consisting of molybdenum as a prim-ary metal alloyed with a secondary metal selected from the group of nickel or cobalt or, alterna-tively, covered by a coating of a ternary alloy consisting of a primary metal selected from the group of molybdenum and tungsten alloyed with two secondary metals selected from the group of cobalt, nickel and iron.

One preferred metal of the electrode supporting the alloy coating is iron, conveniently in the form of mild steel. Another preferred metal is titanium which ris defined throughout this specification as pure titanium or a titanium alloy containing more than 50% 'by weight of titanium, which is known as a titanium base alloy.

The electrodes of the invention may be in the form of wire, tube, rod, planar or curved sheet, perforated sheet, expanded metal, foraminous metal, gauze, porous, cornpacted or fused metal powder.

While the electrodes of this invention can be used as cathodes generally they are particularly useful as hydrogen cathodes, i.e., when hydrogen is deposited on or evolved from them.

When the electrodes of the present invention are used as cathodes in fuel cells, a higher operating voltage, faster reaction rate, improved capacity and better energy efciencies are attained.

Accordingly, We also provide a process of producing electric current from a fuel cell characterised in that the cathode of the fuel cell is .an electrode according to the present invention.

The preferred use of the invention is in electrolytic processes for the production of hydrogen from aqueous electrolytes.

Accordingly, we provide a process of electrolysing an aqueous electrolyte characterised in that hydrogen is evolved electrolytically from a cathode according to the present invention.

The cathodes of our invention are particularly useful for the electrolysis of alkali chloride solution to produce hydrogen, alkali hydroxide and chlorine or, alternatively, to produce alkali chlorate. When hydrogen, sodium hydroxide andchlorine are produced from brine using the cathodes of this-invention, a considerably reduced operating Voltage and improved energy eiiiciency and corrosion resistance are attained.

A preferred embodiment of this invention comprises an electrolytic cell suitable for electrolysis of aqueous sodium chloride solution characterised in that the cathode is an electrode according to this invention.

Another preferred embodiment of the invention is a bipolar electrode consisting of a core of titanium, at least portion of the anodic surface of which is conductively covered by a layer of a noble metal of the platinum group and at least portion of the cathodic surface of which is conductively covered either by a coating of an alloy consisting of a metal selected from the group of molybdenum and tungsten alloyed with iron or, alternatively, covered of Table I. If the composition is kept within the most preferred range shown on the right hand side of 'Fable I, the maximum reduction in hydrogen overvoltage is achieved.

All percentages in this specification are given by weight.

It has been established that electro-deposited layers contain varying amounts, up to several percent, of non-metallic constituents such as oxide. In these low concentrations the metallic oxides present do not affect the overvoltage within the errors of measurement; hence all results are given as fa percentage of the metallic constituents only. The analysis of very thin layers of alloys is fraught with diiculties; consequently the figures stated are thought to lbe :accurate to within i2% only.

TAB LE I Preferred Composition Range Most Preferred Composition Range Alloy AB Primary Secondary Primary Secondary Constituent Ain Constituent B in Constituent A in Constituent B in A B Percent Weight Percent Weight Percent Weight Percent Weight 5 to 70% Mo- (100-A)% Fe 45 to 65% Mo (100-A)% Fe. 5 to 60% W (l0O-A)% Fe 35 to 60% W (100-A)% Fe. 5 to 70% M0 (l00-A)% 0o-"- 45 to 70% Mo (l00-A)% C0. 5 to 65% M0 (100A)% Ni 45 to 58% M0 (100-A)% Ni.

Preferred Range Most Preferred Range Alloy ABC Primary Secondary Tertiary Primary Constituent A in Constituent B in Constituent C in ConstituentA in A B C Percent Weight Percent Weight Percent Weight Percent Weight by :a coating of an alloy consisting of molybdenum and a secondary metal selected from the group of cobalt and nickel or, alternatively, covered by a coating of a ternary alloy consisting of a primary metal selected from the group of molybdenum and tungsten alloyed with two secondary metals selected from the group of cobalt, nickel and iron.

` By a noble metal of the platinum group or platinum metals4 we mean ruthenium, rhodium, palladium, osmum, iridium or platinum or an alloy of two or more of these metals.

Furthermore, we provide an electrolytic cell suitable for assembly into multicells of the kind described in Australian Patent No. 230,799 comprising a bipolar electrode made from a core of titanium, at least portion of the anodic surface of which is covered conductively by a layer of a noble metal of the platinum group and at least portion of the cathodic surface of which is conductively covered either by a coating of an alloy consisting of a metal selected from the group yof molybdenum and tungsten with iron or, alternatively, covered by a coating consisting of an alloy of molybdenum with a metal selected from the group of cobalt and nickel or, alternatively, covered by aco'ating of a ternary alloy consisting of a primary metal selected from the group of molybdenum and tungsten alloyed with two secondary metals selected from the group of cobalt, nickel and iron, which bipolar electrode forms the dividing wall between the cathodic and the anodic compartments of adjacent cells. With cells of the latter type, if desired, as an alternative to the use'of noble metals as anodic surface layers, the opposite side of the titanium sheet to that coated with molybdenum or tungsten alloy may be connected conductively to a graphite anode.

The preferred range of composition for the molybdenum or tungsten alloys is shown on the left hand side 50 to 60% Mo. 50 to 60% Mo. 50 to 60% Mo. 50 to 60% W. 50 to 60% W.

5 to 60% W- The cathodic alloy surfaces of the present invention may be applied to the surface of the metal support by a number of methods known per se. They may be deposited by electroplating, by sintering a mixture of the powdered alloy metals under the application of heat, with or without pressure, by roll-binding, vacuum depositing, metal spraying or rolling the powdered alloy or a mixture of the powdered metals on to the metal sheet, or by painting metallising solution of the alloy on to a metal sheet and subsequent firing, where the metals of the alloy coating are applied in a tinely ydivided form in an organic solvent resin system.

The preferred method of deposition of the alloy is by electroplating.

Numerous compositions of electroplfating baths which may be used for depositing these alloys on metals have been published in the literature. For tungsten alloys, either tungsten trioxide or a soluble tungstate is used together with a salt of the co-depositing metal. Hydroxyorganic acids or their sodium and potassium salts are conventionally added to complex the iron group metals, ammonium chloride or sulphate may be added Vand some baths also comprise inert salts such as sodium or potassium chloride. Molybdenum alloy plating baths are simi-v lar to tungsten baths in composition, with molybdenum trioxide or a soluble molybdate replacing the analogous tungsten compounds. The hydrogen ion concentration of the bath may be adjusted to the desired value with aqueous ammonia or sodium hydroxide solutions. Many modern baths employ citric or tartaric acid or their sodium and/or potassium salts. Plating techniques have been described, e.g., in the following articles: l

A. Brenner, P. Burkhead and E. Seegmiller, Journal Research of the Natl. Bur. Standards, 39, 351 (1947), and T. F. Frantsevich-Zabludovskaya, A. I. Zayats and V. T. Barchuk, Ukrain, Khim. Zhur. 25, 713 (1959).

While these and other known baths provide coatings which are satisfactory for varying periods of time we have found that particularly durable coatings can be prepared from certain compositions.

6 solution o-f fluoroboric acid containing not less than 2% w./v. of iluoroboric acid.

Compared with platinised titanium cathodes the Ticathodes, of the present invention have the advantage Accordingly, we also provide a method of electroplat- 5 of considerably lower capital cost; compared with coning a metal suitable for the construction of solid elecventional iron or steel cathodes they have the advantage trodes with a molybdenum-nickel alloy from a plating that they have a lower hydrogen overvoltage and that bath comprising from 32 to 45 g. of NaMoO4-2H2O, they are more corrosion resistant and consequently that from 10 to 13 g. of NiCl2-6H-2O, from 27 to 40 g. of they are suitable for construction of bipolar electrodes NaaPgOq and from 70 to 100 g. of NaHCO3 per litre of 10 for use in electrolytic multicells, which are a considerable aqueous solution at a (direct) current density from 2 to advance over the prior art of separate iron cathodes and a./drn.2 and a temperature from 40 to 70 C. graphite anodes; nally, compared with a composite bi- We provide further a method of electroplating a metal poilar electrode in which an iron grid or `sheet used as suitable for the construction of solid electrodes with a a cathode is compressed conductively against or welded molybdenum-nickel-cobal alloy from 4a bath containing 15 to the reverse side of a titanium sheet or a platinised tifrom 32 to 45 g. of Na2MoO4-2H2O', from 5.2 to 6.2 g. tanium sheet anode it has the advantage of much simpliof NiCl2-6H2O, from 5.4 to 6.5 g. of CoCl26H2O, from fied construction, greater compactness, simpler mainten- 36 to 54 g. of Na4P2O710H2O, from 70 to 100 g. of ance and freedom from the corrosion 4difficulties result- NaHCOa and from 1.2 to 1.9 g. of N2H4-H2SO4 per litre ing from bi-metallic joints. Yet another advantage of A of aqueous solution at a current density between 2.5 and 20 this invention is that the electrodes can be prepa-red from 15 a./dm.2 and a temperature from 55 to 75 C. existing mold steel electrodes by plating the steel elec- We also provide a method of electroplating a metal trodes after descailing pretreatment. Thus no large capital suitable for the construction 0f Solid electrodes with a expenditure is required for converting existing electrolytic molybdcnum-nickel-iron alloy from a bath containing 32 cells into cells having the reduced cathode overvoltage to g. of Na2MoO4-2H2O, 4 to 5 g. of FeC13-6H2O, 25 ofthe present invention.

5.4 to 6.6 g. of NiCl2-6H2O, 36 to 54 g. of The lowering of the overvoltage on the cathodes of the present invention may be demonstrated in t ure alkali NaiPzOr' 10H20 chloride and iodide solutions or in the `solutioiijs normally 7() t0 100 g, .uf NaHCO3 and 1 2 t0 1,8 g of NgHl-HZSO4 encountered in the electrolyte of diaphragm cells and in at current densities between 5 and15 a./drn.2 and a tem- 30 'ohi'oraie and ioda'fe eeiiS-' When bilJOi-ll' eieC'f-IOCS HC- perature from t0 70 Q cording to the preferred embodiment of this invention As yet another method of e1ectrop1atmg meta1s Suit are assembled into electrolytic multicells, and sodium able for construction of solid electrodes according to a 'ehioride iS e'ieeifoiysed io Produced either, in 'fhe CaSe of further feature of the present invention comprises plating 'die diaphragm Celi, Sodium hydroxide and `ehliorine 0r, titanium 0r a titanium a110y Containing at kast 50% .by 35 in the case of the chloria-te cells, sodium chlorate, current Weight of titanium with a m01ybdenum iron e0,ba1i 111,0y eiiiciencies are obtained which are compara-ble to those from a bath Containing 32 to 45 .g1 .of Na2MuO42H2O, 4 of the conventional diaphragm and chlorate cells. Energy to 5 g. of FeCl3.6H2O, 5.3 to 6.5 g. of CoCl2.6H2O, 36 to eiiiciencies, however, particularly at high current densities, 54 .g uf NMPZOTJOHZO, 7() to 100 g of NaHCOS and are superior to those of the electrolytic'multicetlls in which 1,2 tu 1,3 g of NZpLiHZSO4 at a .current density from 5 40 the titanium is used as a cathode and are as good as or to 15 a/unr2 and a temperature ,between 5() and 70 C. better than those obtained from electrolytic multicells The Surface .of the meten Sheet may .be subjected to with platinised cathode and platinised anode surfaces or pretreatments to facnitate me depositing of the Moy with platinised anodes and conductively connected iron layer and its surface area may be increased by surface Caihoded treatment or by manufacturing the titanium sheet by 45 The reduced hydrogen overvoltage ofthe cathodes of rolling titanium in powder form to produce a compacted die PreSent invention under Praotioai operating eondi'fiOnS Sheet of vast Surface area A number of methods of pre compared with the mean attainable cathode potential of treatment and of increasing the surface area of the metal aged, i-e Weii InSied Steel eiee'frodeS, With nnpia'd sheet are known per Se, Most of these pretreatments titanium electrodes and with platinised titanium electrodes provide satisfactory deposition and adhesion of the alloy 50 iS `'fPPirent from Ta'bie I- It iS Well known and' Was Con- Coating on the titanium Support, but their durability under firme-d during these experiments that rusted steel electrodes prolonged mechanical and chemical attack varies greatly. have the lowest cathode potential which can, in practice, Many coa-tings under practical plant conditions last no be attained from Steel electrodes. longer than a few weeks. We have found that particularly The VoitageS Stated in 'Table II include liquid junction durable deposits of our alloys can be produced ion ti- 55 potentials and the small ohmic potential `drop |of the tanium, which otherwise is difficult to plate durably and column o felectnolyte between the cathode and the tip of satisfactorily, When the titanium is pretreated with fluorothe Luggin capillary and the potential arising from the boric acid. concentration polarisation at the cathode surface and Accordingly we also provide a method of electroplathence are not indicative of overvoltages in the strictly ing titanium to produce the electrodes of the present inscientific sense, but the measurements are strictly comvention characterised by pretreating the titanium with a parable between experiments.

TABLE II [Temperature A60 C.]

Cathode Lowering of potential overvoltage Current Surface composition of plated mild steel Example Composition by versus compared density Electrolvte cathode No. weight standard with rusted a/dm.2 aqueous solution hydrogen mild steel electrode in volts Busted mild steel, not plated (basis for 1 1 comparison). 10

30 10o g./1. NaOH, Tungsten-iron allo;r 2 e 55% W, 45% Fe 1[1) 200 g./l. N aCi.

TABLE IL JCont'inued [Temperature y60 CJ Surface composition of plated mild steel Example Composition by cathode N 0. weight Tuugstenron alloy 3 38% W, 62% Fe Molybdenum-cobalt alloy 4 44% Mo, 56% Co Molybdenum-cobalt alloy 5 67% Mo, 33% Co Molybdenum-cobalt alloy 6 45% Mo, 55% Co Molybdenum-nickel alloy 7 56% M0, 44% N i Molybdenum-nickel alloy 8 49% Mo, 51% Ni Molybdenummiekel alloy 9 50% Mo, 50% Ni Molybdenum-iron alloy 10 55% Mo, 45% Fe Molybdenum-iron alloy 11 62% Mo, 38% Fe Molybdenum-iron-cobalt alloy 12 55% Mo Molybdenum-nickel-iron alloy 13 55% Mo Molybdenum-nickel-eobalt alloy 14 55% Mo Molybdenum-nickel alloy 15 25% Mo, 75% Ni Titanium 130 sheet (unplated) 18 100% Mild steel (rusted) (unplated) 18 Molybdenum-nickel alloy 18 75% Ni, 25% Mo Tungsten-iron alloy 19 52% W, 48% Fe- Tungsten-iron alloy 20 55% W, 45% Fe Tungsten-iron alloy 21 58% W, 42% Fe- Molybdenum-iron alloy 22 50% Mo, 50% Fe i Molybdenum-iron alloy 23 59% Mo, 41% Fe Molybdenum-nickel alloy 24 56% M0, 44% Ni Molybdenum-nickel alloy 25 49% Mo, 51% Ni Molybdenum-cobalt alloy 26 54% M0, 46% Co Molybdenum-cobalt alloy 27 62% Mo, 38% Co Mo1ybdenum-nickeLcoba1t alloy 28 56% Mo Molybdenum-nickel-cobalt alloy 29 55% M0 Molybdenum-nickel-iron alloy. 30 55% Mo Molybdenumobalt-iron alloy 3l 55% Mo Cathode Lowering of potential overvoltage Current versus compared density Electrolytestandard with rusted af'dm.Z aqueous solution hydrogen mild steel electrode in volts 0. 97 0. O8 1 1. 05 0. 15 10 1.09 0. 19 30 0. 90 0. 15 1 0. 96 0. 24 10 0. 99 0. 29 30 0. 91 0. 14 1 0. 98 0. 22 10 1. 01 D. 27 30 0. 93 0. 12 1 1. 0D D. 20 10 1. 03 0. 25 30 0. 90 0. 15 1 0. 95 0. 25 10 0. 97 0. 31 30 0. 88 0. 17 1 0. 92 l). 28 10 0. 94 0. 34 30 0. 90 0. 15 1 0.95 0.25 10 0. 97 O. 31 30 0.93 0. 12 1 0. 99 0. 21 10 1. 02 0. 26 30 0. 91 0. 14 1 1. 02 0. 18 10 1. 07 0. 21 30 0. 92 0. 13 1 0. 99 0. 21 10 1. 02 0. 26 30 0. 90 0. 15 1 0. 95 0. 25 16 0. 98 0. 30 30 0.88 0. 17 1 0. 91 0. 29 10 0. 93 0.35 30 0. 96 0. 09 1 1. 10 0. 10 10 1. 16 0. 12 30 l. 12 l 1. 27 10 1. 36 30 1. 05 0. 07 1 100 g./1. NaOH, 1. 20 0. 07 10 200 g./l. NaCl. 1. 28 0. U8 30 O. 97 0. 15 1 1. 05 0. 22 10 1. 09 O. 27 3U 0. 96 0. 16 1 1. O2 0. 25 10 1. 05 0. 31 30 0. 89 0. 23 1 l. 01 0. 26 10 1. 07 0. 29 30 0. 99 0. 13 1 1. 05 0.22 10 1.08 0. 28 30 0. 93 0. 19 1 0. 98 0. 29 10 1. U0 0.36 30 O. 96 0. 16 1 1. 02 0. 25 10 1. O5 0.31 30 O. 90 0. 22 1 0. 95 0. 32 10 0. 97 0. 39 30 0. 91 6. 21 1 0. 96 0. 31 10 0. 98 0. 38 30 0.90 0. 22 1 0. 98 0. 29 10 1. 02 l). 34 30 0. 92 0. 20 1 0. 98 0. 29 10 1. 01 0.35 30 0. 88 0. 24 1 D. 91 0. 36 10 0. 93 0. 43 30 0.91 0. 21 1 0. 97 0. 30 10 1. 00 0. 36 30 0. 91 0. 21 1 0.97 0. 30 10 1. 00 0. 36 30 0. 92 0. 20 1 D. 99 O. 28 10 1. O2 0. 34 30 Electrolytic cells incorporating electrodes according to the presentinvention will now be described with reference to the accompanying diagrammatic drawings.

In these drawings:

centre of a diaphragm cell at to the electrodes;

FIG. 2 is a vertical cross-section through the centre of a Vchl-oratie cell assembly of the bipolar type;

FIG. 3 is |`a vertical cross-section of the chlorate cell assembly on the line a-a of FIG. 2, and

FIG. 4 is a vertical crosssetion through a diaphragm 5 cell assembly.

The laboratory experiments 1 to 15 were carried out on a model diaphragm cell of the vertical submerged cathode type shown schematically in FIG. 1. The -cell was a glass vessel the ratio of height to width (cross section through cell) to length (plane of electrodes and diaphragm) being approximately 2:1:1. Referring to FIG. 1 of the drawings, the cell walls 101 consisted of glass; all liquid-tight joints were made by silicone rubber gaskets. A graphite anode 102 and the interchangeable cathode 104, insulated from each other, were connected to the opposing electrodes of a source of direct current. Anode and cathode compartment were separated from each other by a permeable porous, polyethylene diaphragm 103. To prevent back diffusion of anode products a relatively large ow of electrolyte through the cell compartments was maintained. Inlets and outlets for feed of electrolyte and discharge of catholyte, hydrogen and chlorine not shown in the sketch were arranged in the manner usual with diaphragm cells of the submerged, vertical cathode ty-pe and known to those skilled in the art.

The -cathode potential was measured by means of a Luggin capillary 105 which penetrated the glass cell Wall at the top of the cell to extend to a position slightly spaced from the centre of the cathode. The Luggin capillary was connected by a salt bridge to an individual calomel reference electrode (not shown) in the usual manner. The electrolyte discharged from the cell contained 100 g. NaOH and 200 g. NaCl per litre. The interchangeable -cathodes were prepared as set out in the examples and a series of determinations was carried out at each selected current density after careful equilibration of experimental conditions. The results shown in Table Il are the means of the replicate determinations.

Referring now to FIGS. 2 and 3 of the drawings, the bipolar -chlorate cell assembly there illustrated consists of two cells A and B identical in size. The outer end of the cell A consists of `a titanium sheet 4 to the inner surface of which a coating 5 of platinum has been applied. The opposite wall of the cell A is constituted by a titanium sheet 6, the inner surface 7 yof which has been etched. The other side of the titanium sheet 6 has a platinum coating 8 applied to constitute the inner wall of the cell B. The opposite wall of the cell B consists of a titanium sheet 9, the inner surface of which has been coated to a depth of approximately 0.002 cm. with an alloy l0 of approximately 45% by weight yof molybdenum and 55% by weight of cobalt. The sheets 4, 6 and 9 are spaced apart t-o form the liquids-tight cells A and B by rectangular polythene washers 11 engaging the sheets yadjacent to the periphery thereof.

An electric conductor 12 is connected to the positive terminal of a source (not shown) of direct current, and a further electric conductor 13 is connected to the negative terminal of the same source. The sheet 4 thus constitutes the anode of the cell A, the cathode being the etched surface 7 of the sheet 6. The platinum coating on the sheet 6 is the anodic surface of the cell B, the cathodic surface being the alloy coating 10. Electrolyte may enter a'nd leave the cells A and B through pipes 14, 15, 16 and 17 which extend through the washers 11. If desired, cell assemblies comprising more than two cells can be constructed in an analogous manner.

The multiple diaphragm cell assembly shown in FIG. 4 consists of two cells C and D identical in size, with porous polytl'lene diaphragms 20 and 21, respectively, dividing the cells symmetrically. The outer wall of the anodic compartment of cell C is constituted by the anode which consists of a titanium sheet 22 to the inside surface of which is applied a coating 23 of platinum. The dividing wall between the cells C and D is a titanium sheet 28, the cathodic surface of which within cell C is a coating 29 of an alloy consisting of approximately 45% by weight molybdenum and 55% by weight cobalt of a thickness of approximately 0.002 cm.

The other side `of the sheet 28 is coated with a lplatinum coating 30 which constitutes the anodic surface of cell D. The cathodic surface of cell D is a coating 31 of an alloy consisting of approximately 45% by weight molybdenum and 55% by weight cobalt, approximately 0.002 cm. thick, applied to the inner surface of the titanium outer wall 32 `of the cell. An electrical conductor 33 connects the sheet 32 to the negative terminal of a source (not shown) of direct current, and a further electrical conductor 34 connects the sheet 22 to the positive terminal of the same source.

The cells C and D are completed in a fluid-tight manner, and the sheets 22, 28 and 32 and membranes 20 and 21 are `positively spaced, apart, by rectangular polyethene washers 35, 36, 37 and 38 which are of similiar shape to the washers 11 lof FIGS. 2 and 3, and extend around the margins of the sheets. A pipe 39 through which electrolyte may be supplied to the cell C, and a further pipe 40 through which chlorine is led off from the cell C, both penetrate the washer 35 on the side of the membrane 20 adjacent to the sheet 22. On the side of the membrane 20 adjacent to the sheet 28, a pipe 41 through which hydrogen may escape from the top Iof the cell and a pipe 42 through which caustic cell liquor may be removed from the bottom of the cell, penetrate the polythene Washer 36. Pipes 43 and 44, respectively, for the supply of electrolyte to and removal of chlorine from the cell D penetrate the upper portion of the polythene washer 37 on the side of the membrane 21 adjacent to the sheet 28. On the other side of the membrane 21, the washer 38 is penetrated by a pipe 45 at the top of the cell for the removal of hydrogen Vand by a pipe 46 iat the bottom of the cell for the removal of caustic cell liquor.

A Luggin capillary 47 penetrates the polythene washer 36 at the top of cell C to extend to a position slightly spaced from the centre of the cathode surface 29. A further Luggin capillary 48 penetrates the polythene washer 38 at the top of cell D to extend to a position slightly spaced from the centre of the cathode surface 31.

Each of these Luggin capillaries is connected by a salt.

bridge to an individual calomel reference electrode (not shown) in the usual manner. These Luggin capillaries and associated calomel electrodes are not part of the cell assembly in the form in which it would be used in commercial operations, but have been included to permit measurements to be made. If desired, cell assemblies com- Iprising more than two compartments can be constructed in an analogous manner. Examples 19 to 31 inclusive were carried out in a cell of the type shown in FIG. 4.

Our invention is now illustrated by, but is not limited to the following examples:

Example 1 Twenty mild steel plates of 1A; in. thickness were subjected to a pretreatment consisting in degreasing with trichlorethylene, drying and treating for 10 minutes at room temperature @012 C.) with 17% w./V. hydrochloric acid. The samples were then rinsed with distilled water and dried in the oven at C.

After the pretreatment they allowed to age by exposure to -the open atmosphere in a chlorine producing factory for 4 weeks. A fine sur-face of rust was formed on the steel during this period. Each aged sample in succession was then made the cathode of an electrolytic cell for the production of sodium hydroxide and chlorine and the cathode potential was measured at three current densities. The potential iof the aged electrodes was lower than that of bright steel untreated or acid treated.

Each of the three results given in Table 1I is the means of these twenty determinations and was used subsequently as a basis for calculation of the lowering of overvoltage in Examples 2 to 15 inclusive.

Example 2 A mild steel sarnple was degreased, acid treated by immersing it in 17% hydrochloric acid for 5 minutes vat 1 l 20 C. and rinsed with distilled water. It was then electroplated in a plating solution of the following composition: 50 g./1. of Na2WO4-2H2O, 7 g./1. of

FeSO4( NH4) 2SO4.6H2O (II) 8.7 g./1. of FeNH4(SO4)2.12H2O(III), 66 g./1. of citric acid and NH4H to pH 8.0 `for 7 minutes at 70 C. at a current density of 10 a./dm.2. A bright metallic deposit was formed. The sample was then made the cathode in a diaphragm cell for the production of sodium hydroxide and chlorine. Cathode potentials of this sample in alkaline brine were measured. Results are shown in Table II.

Example 3 A mild steel plate was acid treated as in Example 2 and electroplated in the following solution: 3.6 g./ 1. of Na2WO4-2H2O, 85.6 g./1. of FeSO4.7H2O, 66 g./ 1. of citric acid and NH4OII to pH 8.0. The current density was 10 .a./dm.2 maintained for 5 minutes at 70 C. A steel anode was used. The sample was then made the cathode in a diaphragm cell for the .production of sodium hydroxide and chlorine. Cathode potentials are recorded in Table II.

Example 4 Example 5 Example 4 was repeated but the current density was maintained at 24 a./dm.2 for a period of 3 minutes. The deposited coating was indistinguishable in appearance from that of Example 4. Results are Stated in Table II.

Example 6 A mild steel plate pretracted as in Example 2 was electroplated in a bath of the yfollowing composition: 155 g./ 1. of CoSO4.7H-2O, 295 g./ 1. of sodium citrate, 206 g./ 1. of Na2MoO4.2H2O and NH4OH to pH 10.5, at a current density of a./dm.2 :for 10 minutes at 25 C. using platinum anodes. A dark deposit was obtained. The sample was then made the cathode in a diaphragm cell ffor the production of sodium hydroxide and chlorine. Cathode potentials are recorded in Table II.

Example 7 A mild steel plate was acid pretreated as described in Example 2 and plated in a bath of the following composition: 40 g./ 1. of Na2MoO4-2H2O, 11.4 g./ 1. of

NiOl2.6H2O

33 g./ 1. of Na4P2O7 and 80 g./ 1. of NaHCO3 using a graphite anode at 70 C. and a current density of 50 a./drn.2 for a period of 2 minutes. The sample was then made the cathode in a diaphragm cell for the production of sodium hydroxide and chlorine. Cathode potentials during electrolysis are shown in Table II.

Example 8 An acid treated .mild steel sample was electroplated in a solution of the following composition: 40 g./ 1. of

Nar/romanzo 11.4 g./ 1. of NiCl2.6-H2O, 33 g./1. of Na4P2O7 and 80 g./ 1. of NaHCO3. A graphite anode was used with a bath temperature of 70 C. A plating current density of 5 a./dm.2 was maintained for a period of 20 minutes. A

light grey metallic electroplate was produced. The sample was then made the cathode in a diaphragm cel-l for the production of sodium hydroxide and chlorine. Cathode potentials are given in Table II.

Example 9 Experiment 8 was repeated but the current density was altered to 50 a./dm.2 maintained for 11/2 minutes. A dark grey lustrous deposit was obtained. The sample was then made the cathode in a diaphragm cell for the production of sodium hydroxide and chlorine. Figures are given in Table II. Comparison of Examples 8 and 9 shows that low discharge potentials for hydrogen were recorded over a wide range of plating current densities.

Example 10 A mild steel plate was pretreated as in Example 2. Electroplating was carried out in a bath of the following composition: 40 g./ 1. of Na2MoO4-2H2O, 9 g./ 1. of

FeCl3.6H2O

27 g./1. of Na4P2O7 .and 75 g./1. of NaHCO3, at 50 C. A graphite anode was used. The sample was plated rfor 30 minutes at a current density of 3 a./dm.2. A light grey metallic deposit was formed. The sample was then made the cathode in a diaphragm cell for the production of sodium hydroxide and chlorine. Results are given in Table II.

Example 11 Example 12 was repeated using, however, a higher current density, 50 a./dm.2 for 4 minutes. A grey metallic deposit of appearance similar to that of Example 10 was obtained.. The electrode was then made the cathode of an electrolytic cell for the production of caustic soda solution and chlorine. The cathode potential obtained is shown in Table II. The Widely differing current densities of Examples 10 and 11 again produced no appreciable difference in hydrogen overvoltage.

Example 12 A mild steel plate was pretreated as in Example 2. It was transferred. to a plating Ibath of the l'following composition: 40 g./1. of Na2MoO4-2H2O, 4.5 g./ 1. of

FeC13.6H2O

5.9 g./ 1. of CoCl2.6H2O, 45 g./1. of Na4P2O7.10H20, 75 g./ 1. of NaHCO3 and 1.5 g./ 1. of N2H4-H2SO4. Plating was carried out at C. and a current density of 5 a./drn.2 for 15 minutes using a graphite anode. The resulting deposit was bright grey in appearance. The

" sample was then made the cathode in a diaphragm cell for the production of sodium hydroxide and chlorine. Results are shown in Table II.

Example 13 A sample of mild. steel plate, acid treated as described in Example 2 was plated in a solution of the following composition: 40 g./ 1. of Na2MoO4.2H2O, 4.5 g./ 1. of FeC13.6H2o, 5.9 g./1. of Nicignzo, 45 g./1. of

75 g./ 1. of NaHCO3 and 1.5 g./ 1. of N2H4.H2SO4. Bath temperature was held at 60 C. while plating was carried out at a cathode current density of 15 a./dm.2 for a period of 6 minutes. A light grey metallic electro-deposit was formed on the mild steel cathode. The sample was then made the cathode in a diaphragm cell'for the production of sodium hydroxide and ch orine. Data are shown in Table II.

Example 14 A mild steel specimen was acid treated as in Example 2. This was electroplated in a solution of the following composition: 32 g./l.k of Na2MoO4-2H2O, V5.7 g./l. of NiCl2-6H2O, 5.9v g./l. of CoCl2-6H2O, 56 g./1. of

13 Na4P2O7-1OH2O, 75 g./l. of NaHCO3 and 1.5 g./l. of N2H4H2SO4 at a current density of 5 a./dm.2 for 15 minutes. The bath temperature was 60 C. and a graphite anode was used. The sample was then made the cathode in a diaphragm cell for the production of sodium hydroxide and chlorine. Cathode potentials are -recorded in Table II.

Example l5 A mild steel plate was acid treated as described in Example 2 and placed in a plating solution of the following composition: 85 g./l. of NiSO4'7H2O, 88 g./l. of sodium citrate, 48 g./l. of Na2MoO4-2H2O and NH4OH to pH 10.5. Electroplating was carried out for minutes at 5 a./dm.2 and 35 C. using a molybdenum anode. The resulting deposit was matt grey. The sample was then made the cathode in a diaphragm cell f-or the production of sodium hydroxide and chlorine. Results are given in Table II.

Example 16 The mild steel gauze cathodes of three industrial scale diaphragm cells of the vertical cathode type were degreased, acid treated, rinsed and plated as described in Example 10. The plating and operating cu-rrents were chosen to be as in Example 10, making the simplifying assumption that the whole of the exposed surface of the cathode gauze is electrically effective. The cathodes were then installed in three industrial cells and run concurrently with three control cells with conventional mild steel electrodes. Measurements of operating voltages under plant conditions were taken over 40 days three times daily. The mean of all measurements :on the controls was 0.20 v. higher than the mean of all the cells with molybdenumiron plated cathodes.

Example 17 The mild steel gauze cathodes of three industrial scale diaphragm cells of the vertical cathode type were degreased, acid treated, rinsed and plated as described in Example 8. The plating and operating cur-rents were chosen to be as in Example 8, making the simplifying assumption that the whole of the exposed surface of the cathode gauze is electrically effective. The cathodes were then installed in three industrial cells and run concurrently with three control cells with conventional mild steel electrodes. Measurements of operating voltages under plant conditions were taken over 40 days three times daily. The mean of all measurement on the controls was 0.27 v. higher than the mean of all the cells with molybdenum-nickel plated electrodes.

Example 18 A rectangular piece of rolled titanium sheet (grade 130 as defined in I.C.I. Brochure Wrought Titanium, 4th edition (1958), page 5, manufactured by Imperial Chemical Industries Ltd., 20 S.W.G.), was treated for a period of 5 minutes at a temperature of 60 C. in a solution of the following composition: 200 mls. conc. HCl, 56 g. of NaF, 142 g. of H3Bo3 per litre of aqueous solution. After rinsing with distilled water the sample was transferred to a strike bath which contained 20 gram/litre of cobalt as the sulphate, and hydrochloric acid was added to give a. pH of from 0.5 to 1.0. The purpose of the pretreatment in a strike bath was to facilitate subsequentdeposition of the alloy. Using the titanium sample as the cathode and a sheet of platinised titanium as the anode, an electrolysing current of 20 amperes/dm.2 -of cathode surface was passed for 3 minutes. The titanium sample was then transferred to an alloy plating bath of the following composition: 12 grams of molybdenum as sodium molybdate, 4 grams of nickel as nickel sulphate, 200 grams Rochelle salt and 50 grams of sodium chloride per litre of solution. Ammonium hydroxide was added to adjust the pH to 10.5 at 37 C., the temperature used for plating. A piece of sheet titanium was plated in this bath for 14 20 minutes at a current density of 1.0 amp/dm.2 using a nickel anode. A lustrous metallic grey deposit about 0.002 cm. thick comprising 25% molybdenum and 75% nickel was obtained.

The electroplated titanium sample was then made the cathode of a chlorate multicell. The cell was a two-cell assembly of the bipolar type as shown schematically in FIGURES 2 and 3. The cell was designed primarily for comparison of electrode materials, the lgreatest attention being given to identical geometrical arrangement and dimensions of the two compartments. By interchanging the components it was demonstrated that the two compartments were geometrically and hydrodynamically equivlent.

Electrolyte, consisting 0f an aqueous solution of 316 g./l. of sodium chloride, to which 6 g./l. of anhydrous sodium chromate were added, was supplied to the cells. The first cell (A), with the platinised titaniurn anode and etched titanium sheet cathode, remained unchanged and undisturbed during the tests, and so served as a control. By changing the cathode 9 of the second cell (B) a direct comparison of cathode materials could be obtained. Results are presented for the following cathode materials:

(a) Etched titanium sheet, which had been etched for 3 days in concentrated A.R. grade hydrochloric acid. The surface of this sheet was hydrided.

(b) Platinised titanium prepared by electroplating titanium sheet-from an alkaline hydroxy-platinate bath to a density of g. platinum per square metre according to methods shown in the prior art.

(c) Mild steel sheet, pretreated by prolonged exposure to atmosphere to produce a rusty surface, the oxide layer being reduced to magnetite during service as a cathode, as is Well known in the prior art.

(d) Sheet titanium metal electroplated with an alloy of molybdenum and nickel, as described above. Results are given in Table III.

The molybdenum nickel plated titanium sheet was then made the cathode of an electrolytic diaphragm two-cell assembly of the construction shown in FIG. 4, the electrolyte in the cathode compartment in this case consisting of an aqueous solution containing 200 g./l. of sodium chloride and g./l. of sodium hydroxide. Measurements of potential were made between the calomel reference electrodes and the coatings 29 and 31 while electrolysis was in progress. The measured potentials were then compared with values obtained when a pure titanium sheet was substituted for the sheet 32, and at 60 C., the values for the molybdenum nickel coated cathode were found to have an overvoltage lower by millivolts for a current density of 1 a./dm.2 and by 220 millivolts for a current density of 10 a.,/dm.2, than foi the pure titanium sheet, as shown in Table II.

As shown in Table III cells using a titanium cathode plated with the molybdenum-nickel alloy exhibited a cell voltage approximately 0.4 volt lower than a cell with a titanium cathode at the lower current density. As a cathode material the molybdenum-nickel electroplated titanium cathode also compared favourably with rusted mild steel, one of the conventional cathode materials for chlorate cells, and with the recently developed platinised titanium.

Example I9 The titanium specimen was etched as described in Example 18 and transferred to a plating bath ofthe following composition: 50 g./l. of Na2WO22H2O, 7 g./l. of FeSO4(NH4)2SO4-6H2O, 8.7 g./l. of

66 g./l. of citric acid and NH4OH to pH 8.0. The bath colour was light brown and darkened on the addition of ammonia for pH adjustment. Steel anodes were used in the electroplating which was carried out at a -cathode current density of a./drn.2 for 7 minutes at 70 C. A bright metallic grey electroplate was produced. The plated sample was then made the cathode in an electrolytic cell for the production of caustic soda and chlorine. Composition of the plating and cathode potential are shown in Table Il.

Example 20 Experiment 19 was repeated with all conditions identical but 'for cathode current density, which was 50 a./drn.2 and plating time, 2 minutes. A bright metallic grey plate was produced. The plated sample was then made the cathode in an electrolytic cell for the production of caustic soda and chlorine. Composition and cathode potential are given in Table II.

Example 2l A piece of titanium was pretreated as described in Example 18 and electroplated in a bath of the following composition: 40 g./l. of Na2M-OO42H2O, 9 g./l. of

Feclg .6I-120 27 Ig/l. of Na4P2O7 -zand 75 g./l. of Nall-ICOS. A mild steel cathode was used with a bath temperature of 50 C. The piece of titanium was electroplated for 30 minutes at a cathode current density of 3 a./dm.2. A bright metallic' electrodeposi-t was formed. The sample wasthen used as a cathode in an electrolytic cell for the production of caustic soda and chlorine. Results are as shown in Table II.

Example 23 Example 22 was repeated, but the plating was carried out at a density of 50 a./dm.2 at 58 C., maintained for 4 minutes. A matt grey deposit was obtained. The sarnple was then made theV cathode in Aa caustic/chlorine dia/` phnagm cell. Results are given in Table II. Although samples 22 and 23 differed in appearance and were prepared at widely diiering current densities, their compositions and overvoltage characteristics ditered little as apparent from Table II. Furthermore, samples prepared at intermediate current densities gave similar cathode discharge potentials.

Example 24 A titanium specimen was etched as in Example 18 and plated in 'a bath ofthe following composition: 40 g./l. of Na2MoO4L2H2O,V 11.4 gL/lpofNiClgfHzO, 33 g./l. of Na4P2O7 and 80 g./l. of Nal-TC03 using a graphite anode at y70" C.V and a current density of 5-0 a./dm.2 for a period of 2 minutes. The plated sample was then made the cathode in an electrolytic cell for the production of caustic soda and chlorine. Cathode potentials during electrolysis are shown in Table II.

Example 25 Example 24 was repeated but the current density was 2.5 a./dm.2, maintained for 40 minutes. Results are shown in Table II.

Example 26 A titanium samplewas pretreated as in Example 18 and electroplated in a bath of the following composition: 32 g./l. of Na2MoO4.2l-I2O, 11.9 g./l. of

COC12.6H2O

40 g./l. of Na4P2O7, 80 g./l. of NaHCOa and 1.5 g./l. of N2H4-H2SO4. Current Ldensity was v2.5 a./dm.2, plating period 30 minutes. A Igraphite anode was used with a bath temperature of 70 C. During plating, the colour of the solution, being initially magenta, became more bluish. A sernibright metallic electroplate was produced. The plated sample was then made the cathode in electrolytic cells for the for the production of caustic soda and chlorine. Data for this alloy appear in Table II.

Example 27 Example 26 was repeated using, however, a current density of 25 a./dm.2 over a period of 3 minutes. A =matt grey deposit was formed. Results are given in Table II. With the alloys of Examples 26 and 2'7, too, the hydrogen overvoltage was attested -little by the plating current density; this was shown by further experiments at intermediate current densities.

Example 28 A ternary alloy of molybdenum, nickel and cobalt was electroplated on etched titanium from a bath of the following compositi-on: 32 g./l. of NazMoOgll-IQO, 5.7 g./l. of NiCl2.6H2O, 5.9 g./l. of CoClgHZO, 45 g./l. of

75 g./l. of NaHCO3 and 1.5 g./l. of N2'H4.H2SO4. A platinised titanium anode was used, with a bath temperature of 60 C. at a current density of 5 :1 /dm.2 for 15 minutes to produce a light grey metallic deposit. The plated sample was then made the cathode in an electrolytic cell for the production of caustic soda and chlorine. Data for this alloy are shown in Table II.

Example 29 Example 28 was then repeated using a cathode current density of 15 a./dm.2. The appearance of the plate was similar to that of Example 29 but it exhibited poorer adherence 'around the edges of the sample. Results are given in Table II.

Example 30 A titanium sample was etched as described in Example 18 and plated in the following solution: 40y g./l. of

4.5 g./l. of FeCl3.6H2O, 5.9 g./l. of NiCl2.6I-I2O, 45 g./l. of Na4P2O7-10H2O, 75 g./l. of NaHCO3 and 1.5 g./l. of N2H4.H2SO4. The bath temperature was 60 C., current density was 15 a./dm.2 maintained for 6 minutes and 'a graphite anode was used. A bright metallic deposit was formed. The plated sample was then made the cathode in an electrolytic cell for the production of caustic sodav and chlorine. Cathode potentials in caustic brine are given in Table II.

Example 31 A titanium sample'was pretreated as in Example 18. A ternary alloy of molybdenum, iron and `cobalt was 17 electroplated on to the etched titanium from the following solution: 40 g./l. of Na2MoO4-2H2O, 4.5 g./l. of FeCl3.6H2O, 5.9 g./l. of CoCl2.6H2O, 45 g./l. of

75 g./l. of Nal-ICOS and 1.5 g./l. of N2H4tH2SO4. A platinised titanium anode was used with bath temperature 60 C. The plating current density was 5 a./dm.2 for 15 minutes. The resulting deposit was light grey. The plated sample was then made the cathode in an electrolytic cell for the productio-n of caustic soda and chlorine. Cathode potentials for this alloy are shown in Table Il.

What we claim is:

1. An electrolytic cell suitable for assembly into multicells comprising a bipolar electrode made from a core of titanium, at least a portion of the anodic surface of which is covered con-ductively by a layer of a noble metal of the platinum group and at least a portion of the cathodic surface of which is conductively covered by a coating of an alloy consisting of a metal selected from the group consisting of from 5 to 70% `of molybdenum and from 5 to 60% of tungsten, said metal being alloyed with iron, which bipolar electrode forms the dividing wall between the cathodic and the anodic compartments of adjacent cells.

2. An electrolytic cell suitable for assembly into multicells comprising a bipolar electrode made from a core of titanium, at least a portion of the `ano-dic surface of which is conductively covered by a layer of a noble metal of the platinum group and at least a portion of the cathodic surface of which is conductively covered by a coating consisting of an alloy of molybdenum with a metal selected from the group consisting of from 95 to 30% of cobalt and from 95 to 35 of nickel, which bipolar electrode forms the dividing wall between the cathodic and anodic compartments of adjacent cells.

3. An electrolytic cell suitable for assembly into multicells comprising a bipolar electrode made from a core of titanium, tat least a portion o-f the anodic surface of which is covered conductively by a layer of a noble metal of the platinum group and at least a portion of the cathodic surface of which is conductively covered by a coat-ing of a ternary alloy consisting of from 5 to 60% of Ia primary metal selected from the group `consisting of molybdenu-m and tungsten, said primary metal being alloyed with two metals selected from the group consisting of cobalt, nickel and iron, which bipolar electrode forms the dividing wall between the cathodic and the anodic compartments of adjacent cells.

4. An electrode comprising a support formed from a metal selected from the group consisting of mild steel, titanium and a titanium base alloy, at least a portion of the surface of which is conductively covered by a coating of an alloy consisting of a metal selected from the the group consisting of from 5 to 70% of molybdenum and from 5 to 60% of tungsten, said metal being alloyed with iron.

5. An electrode comprising a support formed from a `metal selected from the group consisting of mild steel, titanium and a titanium base alloy, at least a portion of the surface of which is conductively covered by a coating of an alloy consisting of molybdenum lalloyed with a secondary metal selected from the group consisting of from 95 to 35 of nickel and from 95 to 30% of cobalt.

6. An electrode comprising a support formed from a metal selected from the group consisting of mild steel, titanium and a titanium base alloy, at least a portion of the surface of which is conductively covered by a coating of a ternary alloy consisting of from 5 to 60% of a primary metal selected from the group consisting of molybdenum and tungsten, said primary metal being alloyed with two metals selected from the group consisting of cobalt, nickel and iron.

7. An electrode according to claim 4 characterised in that the metal ofthe support is mild steel.

8. An electrode according to claim 5 characterised in that the metal of the support is mild steel.

9. An electrode according to claim 6 characterised in that the metal of the support is mild steel.

10. An electrode according to claim 4 characterised in that the metal of the support is titanium.

11. An electrode according to claim 5 characterised in that the metal of the support is titanium.

12. An electrode according to claim 6 characterised in that the metal of the .support is titanium.

13. An electrode according to claim 4 where the content of molybdenum is between 45 and 65%.

14. An electrode according to claim 4 where the content of tungsten is between 35 and 60% by weight.

15. An electrode according to claim 5 characterised in that the coating contains between 5 and 70% molybdenum and between and 30% of cobalt.

16. An electrode according to claim 5 characterised in that the coating contains between 45 and 70% of molybdenum and between 55 and 30% of cobalt.

17. An electrode according to claim 5 characterised in that the coating contains between 5 and 65% of molybdenum and 95 to 35% of nickel.

1S. An electrode according to claim 5 characteristed in that the coating contains between 45 and 58% of molybdenum and between 55 and 42% of nickel.

19. An electrode according to claim 6 characterised in that the coating contains between 50 and 60% of the metal slected from the group consisting of molybdenum and tungsten.

20. A bipolar electrode consisting of a core of titanium, at least a portion of the anodic surface of which is conductively covered by a layer of a noble metal of the platinum -group and at least a portion of the cathodic surface of which is conductively covered by 'a coating of an alloy consisting of a metal selected from the group consisting of from 5 to 70% of molybdenum and from 5 to 60% of tungsten, said metal being alloyed with iron.

21. A bipolar electrode consisting of a core of titanium, at least a portion of the anodic surface of which is conductively covered by a layer of a noble Imetal of the platinum group and at least a portion of the cathodic surface of which is conductively covered by a coating of an alloy consisting of molybdenum and a secondary metal selected from the group consisting of from 95 to 30% of cobalt and from 95 to 35% of nickel.

22. A bipolar electrode consisting of a core of titanium, at least a .portion of the anodic surface of lwhich is conductively covered by a layer of a noble metal of the platinum group and at least a portion of the cathodic surface of which is conductively covered by a coating of a ternary alloy consisting of from 5 to 60% of a primary metal selected from the group consisting of molybdenum and tungsten, said primary metal being alloyed with two metals selected from the group consisting of cobalt, nickel and iron.

23. An electrolytic cell having a cathode formed from a metal selected from the group consisting of mild steel, titanium and a titanium base alloy, at least a portion of the surface of which is conductively covered by a coating of an alloy consisting of a primary metal selected from the group consisting of from 5 to 70% of molybdenum and from 5 to 60% of tungsten, said primary metal being alloyed with iron.

24. An electrolytic cell having a cathode formed from a metal selected from the group consisting of `mild steel, titanium and a titanium base alloy, at least a portion of the surface of which is conductively covered by a coating of an alloy consisting of molybdenum as a primary metal alloyed with a secondary metal selected from the group consisting of from 95 to 35% of nickel and from 95 to 30% of cobalt.

25. An electrolytic cell having a cathode formed from a metal selected from the group Aconsisting lof mild steel, titanium and a titanium base alloy, at least a portion of the surface of which is conductively covered by a coating of a ternary alloy consisting of from 5 to 60% of a primary metal selected from the group consisting of molybdenum and tungsten, said primary metal being alloyed with two metals selected from the group consisting of cobalt, nickel and iron.

, References Cited bythe Examiner UNITED STATES PATENTS JOHN H. MACK, Primary Examiner. D. R. JORDAN, Assistant Examiner. 

6. AN ELECTRODE COMPRISING A SUPPORT FORMED FROM A METAL SELECTED FROM THE GROUP CONSISTING OF MILD STEEL, TITANIUM AND A TITANIUM BASE ALLOY, AT LEAST A PORTION OF THE SURFACE OF WHICH IS CONDUCTIVELY COVERED BY A COATING OF A TENARY ALLOY CONSISTING OF FROM 5 TO 60% OF A PRIMARY METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN, SAID PRIMARY METAL BEING ALLOYED WITH TWO METALS SELECTED FROM THE GROUP CONSISTING OF COBALT, NICKEL AND IRON. 